A boat takes 3.10 h o u r s to travel 10.0 k m down a river, then 6.50 h o u r s

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A boat takes 3.10hours to travel 10.0km down a river, then 6.50hours to return. How fast is the river flowing?style="color: rgb(51, 51, 51); font-family: arial, helvetica, clean, sans-serif; font-size: 13px; line-height: 16px;">style="color: rgb(51, 51, 51); font-family: arial, helvetica, clean, sans-serif; font-size: 13px; line-height: 16px; background-color: rgb(244, 249, 255);">style="display: inline-block; position: static; border-width: 0px; border-left-style: solid; padding: 0px; margin: 0px; vertical-align: -1.2px; overflow: hidden; width: 0px; height: 13.5px;">style="display: inline-block; position: static; border: 0px; padding: 0px; margin: 0px; vertical-align: 0px; width: 0px; height: 35px;">class="mi" id="mathjax-span-24">class="mi" id="mathjax-span-23">class="mi" id="mathjax-span-22">class="mi" id="mathjax-span-21">class="mi" id="mathjax-span-20">class="mrow" id="mathjax-span-19">class="texatom" id="mathjax-span-18">class="mrow" id="mathjax-span-17">style="position: absolute; border: 0px; padding: 0px; margin: 0px; vertical-align: 0px; clip: rect(20.7px 16250px 38.2px -8.6px); top: -35px; left: 0px;">style="display: inline-block; position: relative; border: 0px; padding: 0px; margin: 0px; vertical-align: 0px; width: 38px; height: 0px; font-size: 16px;">style="border: 0px; padding: 0px; margin: 0px; max-width: none; max-height: none; vertical-align: 0px;">class="mathjax" id="mathjax-element-3-frame" role="textbox" aria-readonly="true">class="mathjax_preview">class="type-specific" type="tex">class="replace-insert done" inserttype="units" id="yui_3_3_0_23_137877345380043">style="color: rgb(51, 51, 51); font-family: arial, helvetica, clean, sans-serif; font-size: 13px; line-height: 16px; background-color: rgb(244, 249, 255);">style="display: inline-block; position: static; border-width: 0px; border-left-style: solid; padding: 0px; margin: 0px; vertical-align: -1px; overflow: hidden; width: 0px; height: 13.3px;">style="display: inline-block; position: static; border: 0px; padding: 0px; margin: 0px; vertical-align: 0px; width: 0px; height: 35px;">class="mi" id="mathjax-span-15">class="mi" id="mathjax-span-14">class="mrow" id="mathjax-span-13">class="texatom" id="mathjax-span-12">class="mrow" id="mathjax-span-11">style="position: absolute; border: 0px; padding: 0px; margin: 0px; vertical-align: 0px; clip: rect(20.7px 16250px 38px -8.7px); top: -35px; left: 0px;">style="display: inline-block; position: relative; border: 0px; padding: 0px; margin: 0px; vertical-align: 0px; width: 21px; height: 0px; font-size: 16px;">style="border: 0px; padding: 0px; margin: 0px; max-width: none; max-height: none; vertical-align: 0px;">class="mathjax" id="mathjax-element-2-frame" role="textbox" aria-readonly="true">class="mathjax_preview">class="type-specific" type="tex">class="replace-insert done" inserttype="units" id="yui_3_3_0_23_137877345380039">style="color: rgb(51, 51, 51); font-family: arial, helvetica, clean, sans-serif; font-size: 13px; line-height: 16px; background-color: rgb(244, 249, 255);">style="display: inline-block; position: static; border-width: 0px; border-left-style: solid; padding: 0px; margin: 0px; vertical-align: -1.2px; overflow: hidden; width: 0px; height: 13.5px;">style="display: inline-block; position: static; border: 0px; padding: 0px; margin: 0px; vertical-align: 0px; width: 0px; height: 35px;">class="mi" id="mathjax-span-9">class="mi" id="mathjax-span-8">class="mi" id="mathjax-span-7">class="mi" id="mathjax-span-6">class="mi" id="mathjax-span-5">class="mrow" id="mathjax-span-4">class="texatom" id="mathjax-span-3">class="mrow" id="mathjax-span-2">style="position: absolute; border: 0px; padding: 0px; margin: 0px; vertical-align: 0px; clip: rect(20.7px 16250px 38.2px -8.6px); top: -35px; left: 0px;">style="display: inline-block; position: relative; border: 0px; padding: 0px; margin: 0px; vertical-align: 0px; width: 38px; height: 0px; font-size: 16px;">style="border: 0px; padding: 0px; margin: 0px; max-width: none; max-height: none; vertical-align: 0px;">class="mathjax" id="mathjax-element-1-frame" role="textbox" aria-readonly="true">class="mathjax_preview">class="type-specific" type="tex">class="replace-insert done" inserttype="units" id="yui_3_3_0_23_137877345380028">style="color: rgb(51, 51, 51); font-family: arial, helvetica, clean, sans-serif; font-size: 13px; line-height: 16px; background-color: rgb(244, 249, 255);">

Explanation / Answer

t1 = d/v+vr ==> v+vr = d/t1

t2 = d/v-vr ==> v-vr = d/t2

2*v = d/t1 + d/t2 = 4.76

v = 2.382 km/h

vr = d/t - v = 0.843 km/h

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